An interposer is a device having electrically conductive vias that is inserted between one or more integrated circuits. Typically, an interposer is constructed from an epoxy resin substrate. Through holes are opened in the epoxy resin substrate, and then either filled with conductive paste or subjected to an electrolytic plating process to thereby form the electrically conductive vias.
A carrier, such as a printed circuit board, is inserted between the interposer and the integrated circuits. The integrated circuits are electrically coupled to each other via the carrier and the electrically conductive vias.
However, the resulting electronic devices formed using such interposers may be thicker than desirable. Consequently, there has been a demand for thinner interposers to be used in miniaturized electronic devices. Therefore, new interposers constructed from silicon have been devised. Due to the hardness of silicon, the thickness thereof as an interposer can be less than that of an epoxy resin interposer, resulting in a thinner and smaller electronic device. In addition, wiring layers may be directly deposited on the silicon, potentially eliminating the need for a carrier between an interposer and an integrated circuit.
One such interposer is disclosed in U.S. Pat. No. 7,678,685 to Sunohara et al. Sunohara et al. discloses an interposer including a substrate made of an inorganic material. Through wiring including conductors is embedded in through holes. The interposer also includes an upper wiring and/or a lower wiring. The through wiring, the upper wiring, and the lower wiring are respectively formed on preliminary wiring patterns that are formed on layers made of an insulating material applied to at least wiring forming parts of the substrate.
Another interposer is disclosed in U.S. Pat. Pub. 2007/0020914 to Higashi. Higashi discloses a method of manufacturing interposer wherein a first through hole is formed in a semiconductor substrate and a first insulating layer is formed on the entire surface of the semiconductor substrate. First wiring layers connected to each other via an outer through conducting portion provided on the inner surface of the first through hole are formed on both sides of the semiconductor substrate. A second insulating layer is formed which covers the first wiring layers on both sides of the semiconductor substrate and the outer through conducting portion on the inner surface of the first through hole. The second insulating layer has a structure in which a second through hole is provided in a central portion of the first through hole. Second wiring layers connected to each other via an inner through conducting portion provided in the second through hole are formed on the second insulating layer on both sides of the semiconductor substrate.
Due to recent developments of integrated circuits having a large number of pins arranged in a fine pitch array, there is now a demand for silicon interposers with multiple wiring layers thereon to accommodate these integrated circuits. Consequently, methods of producing silicon interposers with multiple wiring layers are needed.